Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $234.80   13.844%   $267.3057   $267.31   $267.30   $267.30  
  Purchase #2 $138.43   6.340%   $147.2065   $147.21   $147.20   $147.20  
  Purchase #3 $106.79   5.650%   $112.8236   $112.82   $112.80   $112.80  
  Purchase #4 $240.82   7.650%   $259.2427   $259.24   $259.25   $259.20  
  Purchase #5 $198.56   12.746%   $223.8685   $223.87   $223.85   $223.90  
  Purchase #6 $105.76   6.786%   $112.9369   $112.94   $112.95   $112.90  
  Purchase #7 $231.51   12.634%   $260.759   $260.76   $260.75   $260.80  
  7 purchase totals = $1,256.67       $1,384.1429   $1,384.15   $1,384.10   $1,384.10